Buck and boost converters are energy-efficient (e.g., up to 95% for integrated circuits) switch-mode power supplies with a variety of applications. For example, buck converters can convert battery voltages (e.g., 12 volts to 24 volts) in a laptop down to a few volts (e.g., 2.5 volts to 5 volts) needed by a central processing unit (“CPU”).
FIG. 1 is a schematic circuit diagram of a buck converter 100 in accordance with the prior art. As shown in FIG. 1, the buck converter 100 includes a constant on-time (Ton) controller 102 and a switching circuit 104 coupled between an input voltage (Vin) and a reference voltage (Vref) (e.g., the ground). The switching circuit 104 includes a first switching transistor 112a (commonly referred to as the high-side switch) and a second switching transistor 112b (commonly referred to as the low-side switch) coupled in series. The first and second switching transistors 112a and 112b individually include a body diode 114a and 114b, respectively. The buck converter 100 also includes an inductor 106, a capacitor 108, and a load 110 (e.g., a CPU) in parallel to the capacitor 108.
In operation, the constant Ton controller 102 turns on the first switching transistor 112a for a constant period of time to supply a switching voltage (Vsw) to charge the inductor 106 and the capacitor 108 during a first period. Subsequently, the constant Ton controller 102 turns off the first switching transistor 112a and turns on the second switching transistor 112b to allow current to freewheel around the inductor 106, the capacitor 108, and the second switching transistor 112b. As discussed in more detail below, the present inventors have recognized that the frequency of the output voltage (Vo) varies as the input voltage (Vin) varies when the constant Ton controller 102 is coupled directly between the input voltage (Vin) and the ground. Such frequency variations can adversely affect performance of the load 110. Accordingly, several improvements in at least reducing such frequency variations may be desirable.